Gas turbine engine with governor drive from power turbine shaft



3,2 DRIVE INVENTQR DWARD A. HULBERT ATTORNEYS United States Patent ice 3,277,649 GAS TURBINE ENGINE WITH GOVERNR DRIVE FROM POWER TURBINE SHAFT Edward A. Hulbert, Grosse Pointe, Mich., assignor to Continental Aviation and Engineering Corporation, Detroit, Mich., a corporation of Virginia Filed May 28, 1964, Ser. No. 370,900 3 Claims. (Cl. 6039.16)

This invention relates to turboshaft engines and more particularly relates to a governor drive for the power turbine in a free turbine engine.

The free turbine engine is characterized by two mechanically independent rotating systems. The first rotating system, called the gas generator or gasifier consists of a compressor and a turbine which furnishes the power to drive the compressor. The second rotating system consists of the power turbine, connecting shafting, a speed reducton gear, and the useful load. This second rotating system is actuated by the hot gas furnished by the first system and has no mechanica] connection thereto. As a result, the free turbine engine includes an inherent hazard which is not present in any previous form of power plant. If a failure occurs in the drive train between the free turbine and the load, a sudden loss of load will result while the gas generator is still producing hot gas at the same energy level as =before the failure. Since the load is then disconnected from the turbine, the full energy of the gas is absorbed only by the acceleration of the free turbine and the portion of the drive train still connected thereto. This acceleration is a maximum at the instant of load release and decreases to zero at the turbine speed where the turbine blade velocity is equal to the gas velocity. This final or equilibrium speed is far beyond the safe operating speed of any turbine designed with light weight as an objective.

In most free turbine engines, the turbine governor drive train originates at a point in the reducton gear train so as to minimize the speed reducton required to drive the governor. However, the result of an arrangement of this kind is that any failure between the turbine and output shaft of the reducton gear resulting in a loss of the load will render the governor inoperative to prevent overspeed, and will probably result in a turbine disc burst with destructive efiects to the engine and surrounding objects.

In well designed and constructed light weight turbines, mechanical reliability of components should be such that many thousands of hours of field operation should be attained for each incident of mechanical failure, -but this particular type of failure, a turbine disc burst, is so destructive that it should be avoided to a greater degree than may be possible by ordinary reliability improvement means.

It is therefore the priucipal object of the present invention to greatly reduce the probability of turbine burst in a free turbine engine. This object is preferable to other common solutions to the free turbine burst problem; that of providing containment barriers to catch the fragmeuts of deliberately weakened blades, or that of provding sturdier barriers to contain the fragments of burst dscs. Such solutions add needless weight and reduce the desirable stress margins.

It is an object of the present invention to prevent turbine burst by rendering it statisticallyimprobable that excessive turbine overspeed will ever be experienced.

This object is preferable to that of minimizing damage resulting from excessive overspeed.

It is an object of the present invention to provide a power turbine governor and governor drive train which will substantially reduce the probability of turbine burst or excessive turbine speed without the addition of weight 3,277,649 Patented Oct. 11, 1966 or equipment beyond that presently required for conventional governor drive means.

The present invention achieves this object by providing a governor drive which is mechanically independent of the power transmitting gear train. As a result of this construction of the governor drive train, it is statistically irnprobable that destructive turbine overspeed will ever occur. Such an occurrence would require the simultaneous failure of the main power train and either the power turbine governor or its own independent drive train.

If either the power turbine governor or its drive train fails the governor will slow down and thereby cause the fuel control to deliver more fuel. The additional fuel will speed up the gas generator, the power turbine, and the output shaft. This should signal the pilot or operator of a malfunction in the engine and that the gas generator speed should be re-duced by resetting the condition lever or the engine shut down. A fully alert operator should react to this situation in a few seconds. However, even if he should take two full minutes to react, and assuming that the reliability of the governor and its drive train is such that failures occur once each 100,000 hours of field operation, his two minutes reactance time represents only one three-millionth of the assumed time between failures. The only way in which destructive overspeed of the power turbine could occur would in as the result of a second failure in the main power train somewhere between the turbine and the useful load during the same two-minute reactance time of the operator. Assuming that the reliability of the main power train is the same as for the governor and its drive train, that is, one failure for each 100,000 hours of field operation, for this train to fail in any two minute period means that it will also fail in one three-millionth (.333 10* of the time between failures.

It can be seen that simultaneous failure of both trains wthin the same twominute reactance period will occur only in the prbportion of the total engine running time represented by the product of these two very small numbers. This product is (.333 10 which is the incredibly small number of .111 10- This means that about 300 billi0n field service engine running hours will elapse between each incident of uncontrolled overspeed of a power turbine. Even if the reliability of each train were only one thirty-third as high as assumed, that is one failure for each 3000 running hours, a completely unsatisfactory reliability, there would still be 275 million hours of field service operation between incidents of uncontrolled overspeed of a power turbine. This would -be the equivalent to running 55,000 engines 1000 hours a year for 5 years between incidents of uncontrolled overspeed of the power turbine. It can be seen, therefore, that the -fundamental principle of providing two independent systems will completely nullify the inherent hazard of turbine bursts in a free turbine engine.

Others objects and advantages of the present invention will be more readily apparent from the following detailed description of a preferred embodiment thereof. The description makes reference to the drawing in which FIG. 1 is a side view taken through an internal combustion turbine engine with various parts breken away and others shown in cross-section for purposes of clarity; and

FIG. 2 is an enlarged fragmentary longitudinal crosssectional view of the governor drive train in the engine of FIG. l.

Referring to the drawings in detail FIG. 1 shows a turboshaft engine adapted to drive the rotors in .a conventional helicopter aircraft. The engine includes a gasifier generally indicated at 11 and comprising a compressor section, generally indicated at 10, a combustor 12, and turbines 14. The compressor 10 directs compressed air into the toroidal-shaped annular comb-ustor 12. The hot gas from the comhustor drive the pair of axially mounted turbines 14. The entire engine is mounted in a conventional engine housing 15.

The engine further inciudes a power turbine section 13 comprising a power turbine 16 mounted rearwardly of the turbines 14 and the oombustor 12 in an anuuiar shroud 17 and fixed to a hollow drive shaft 18. The drive shaft, as shown in FIG. 2, is supported in a forward power turbine hearing 20 and an aft power turbine hearing 22. A quill drive shaft 24 is splined to the end of the shaft 18 and is supported on i ts own rearward-bearing (not shown). An annu1ar la-byrinth seal 28 surrounds the shaft 18 adjacent the turbine 16. The quill drive shaft 24 is connected through a suitable reduotion gear train in the rear section 30 of the engine to the helicopter rotors (not shown) The governor drive, indicated generally at 36 and shown in detail in FIG. 2, is positioned hetween the forward and aft bearings 20 and 22. The drive includes a primary bevel gear 38 mounted in its own hearing 40 independent of the power turbine shaft bean'ngs. The bevel gear 38 is connected to a hollow shaft 42 which is concentric to and splined to the drive shaft 18 inunediate ly beyond the forward hearing 20. The inner diameter of the connecting shaft 42 is suhstantially larger than the ut-erdiarneter of the drive shafit 18. As a result, a considerable radial clearance is provided between these shafts 18 and 42.

An engaging bevel gear 44 mounted on a shaft 46 is rotated by the primary gear 38. The shaft 46 is supported in a hearing 48 and encased in a housing 50. The lower end of the shaft is connected hy a second hevel gear arrangement 52, 53 to the power turbine governor at 54.

It can be seen that the emhodirnent of the invention shown in F168. 1 and 2 provides a maximum of indepedence between the governor drive and the power train. Loss of 1oad at any point in the power train from the reduction gear :to the helicopter rotor shaft will clearly not impair the operaton of the governor. In fact, the isolation of the governor drive is so complete that it can be reasoned that only two possible failures could occur which could in any way jeopardze the governor drive and also result in loss of load. The first of these possible failures is the failureof the aft power turbine hearing 22. In the event of such fail-" ure, the turbine will pivot around the forwandbe-aring 20 and the turbine hlades will scrape on the shroud 17 before damaging the governor drive. Even if this err-atic motion should produce a broken drive shaft 18, the governor drive will remain intact due to the radial clearance hetween the sha*fits 18 and 42.

In the case of the other prime failure, that of the forward power turbine hearing 20, the turbine assembly will tilt ahout the aft hearing 22. In this event, the lahyrinth sea1 28 will function as a hearing while the turbine blads wili scrape on the turbine shroud 17. The independent hearing 40 on the governor drive gear 38 should continue to adequately support the governor drive gear. The effectiveness of the present independent governor drive can be greatly increased by employing a -fast acting governor. Systerns of this type which might he employed inolude direct actng power turbine governors, acoelerom eter type fuel cutofis, and compound power turbine governors.

It will he apparent to those skjlled in the art to Which this invention pertains that various changes or modifications in the construction of the component parts nay be made without departing frm the-spirit o the inventi on or from the scopeof the appendedclaimsm 11. A tree turbine engineassembly-comprising (b) a power turbine assembly including a power turbine driven hy the products of combustion issuirxg frorrn said gasifier and a shaft portion,

(c) a power train including a power shaft and means drivingly connecting said power shaft to said power turbine shaft portion,

(d) a governor assembly adapted to sense rotational speed of said power turbine,

(e) said governor assemhiy ineluding a governor drive and means independent of said means drivngly connecting said power shaft to said power turbine shaft portion to .drivingly connect said governor drive to said power turbine shaft port-ion,

(f) said last rrientioned connecting means comprising a hollow shaft concentrie to and splined to said power turbine shaft portion and engaging gear means oarried hy said hollow shaft and said governor drive,

(g) axially spaced hearing means rotatably supporting said power turbine shaft in fixed structure, and (h) hearing means spaced intermediate said first mentioned hearing means and rotatably supporting said hollow shaft in fixed structure. 2. The turbine assembly as defined in claim 1 and in which (a) a portion only of the axial length of said hollow shaft heing splined to said power turbine shaft,

(b) said intermediate spaced hearing means rotatably supportng the unsplined portion of said hollow shaft, said hearing mernher encompassing said unsplined portion of said hollow shaft.

3. A free turbine engine assembly comprising (a) a gasifier,

(b) a power turbine assemhly ineluding a power turbine driven by the products of combustion issuing fr0m said-gasifier and a shaft portion,

(c) means rotatahly supporting said power turbine assemhly and including a first hearing member supporting said shaft portion in fixed structure adjaeent said power turbine and a second hearing member supporting -said shaft portion in fixed structure at point axia.ily spaced fron1 said first hearing memher,

(d) a power train inchiding a power shaft and means drivingly connecting said power shaft to said power turbineshafit portion outside of said hearing mem hers,

(e) a governor assemhly adapted to sense rotational speed of said power turbine and regulate uel delivery to said gasifier in response to changes in the rotat=onal speed of said power turbine,

(f), said governor. assernb ly including a governor drive and means drivingly connecting said governor drive to said power turbine shaft,

(g) said last -rnentioned means comprisinga hollow shaft conoentric to and splined to said power turbine shaft portion intermediate said first and second beat ing memhers and engaging gear means carried by said hollow shaft and said governor drive,

(h) said hollow shaft having an unsplined portion radially o twrdly spaced trom said power turbine shaft portion and a hearing means positioned intermediate said first and second hearing memhers and s'upporting said unsplined portion in fixed structure.

References Cited by the Examiner 6/1962 Hurtle 60-39.16

JULIUS E; WEST, Prmafy Examine'r. 

1. A FREE TURBINE ENGINE ASSEMBLY COMPRISING (A) A GASIFIER, (B) A POWER TURBINE ASSEMBLY INCLUDING A POWER TURBINE DRIVEN BY THE PRODUCTS OF COMBUSTION ISSUING FROM SAID GASIFIER AND A SHAFT PORTION, (C) A POWE TRAIN INCLUDING A POWER SHAFT AND MEANS DRIVINGLY CONNECTING SAID POWER SHAFT TO SAID POWER TURBINE SHAFT PORTION, (D) A GOVERNOR ASSEMBLY ADAPTED TO SENSE ROTATIONAL SPEED OF SAID POWER TURBINE, (E) SAID GOVERNOR ASSEMBLY INCLUDING A GOVERNOR DRIVE AND MEANS INDEPENDENTLY OF SAID MEANS DRIVINGLY CONNECTING SAID POWER SHAFT TO SAID POWER TURBINE SHAFT PORTION TO DRIVINGLY CONNECT SAID GOVERNOR DRIVE TO SAID POWER TURBINE SHAFT PORTION, (F) SAID LAST MENTIONED CONNECTING MEANS COMPRISING A HOLLOW SHAFT CONCENTRIC TO AND SPLINED TO SAID POWER TURBINE SHAFT PORTION AND ENGAGING GEAR MEANS CARRIED BY SAID HOLLOW SHAFT AND SAID GOVERNOR DRIVE, 